DESCRIPTION: Objectives. Two competing views for how the immune system resolves an acute hepatitis B virus (HBV) infection have been proposed. One, based on previous experiments in chimpanzees, postulates that cytokines are able to "non-cytolytically" cure hepatocytes of all viral DNA, including covalently closed circular viral DNA (cccDNA), the nuclear transcriptional template for HBV; thus, death of infected hepatocytes is unnecessary to cure the infection. The other, supported by the findings of our groups using the woodchuck and duck models of HBV, proposes that cccDNA is eliminated by a combination of hepatocyte death plus loss during one or more rounds of proliferation of surviving hepatocytes to restore liver mass. However, the amount of hepatocyte destruction in the chimpanzee experiments was not determined. And, in all three models, it is unclear if the timing of hepatocyte destruction and proliferation correlates with cccDNA loss. To determine this, we will use an innovative approach to quantify the time course of cumulative hepatocyte proliferation during resolution of HBV infection. This approach uses unique virus-host cell DNA integration sites to mark individual cells and to monitor their fate during the course of infection. These data will be correlated with the loss of viral replicative intermediates and cccDNA from the liver, changes in the percentage of infected hepatocytes and activation of Kupffer cells, decreases in viremia and the appearance of protective antibodies detected in immune complexes, as well as histological measures of hepatocyte death. We will also measure increases in cytokine expression in the liver and serum, as well as changes in liver gene expression for markers of the immune response. Cumulatively, these data will provide a comprehensive picture of the events occurring in the liver and serum during acute resolving HBV infection and will allow us to determine whether the primary driving force of viral clearance is destruction, or cytokine mediated non-cytolytic "curing", of infected hepatocytes. This distinction has profound implications for the design of new antiviral therapies. Relevance. HBV is a major worldwide health problem: >350 million people have chronic infections that result in a 25-50% lifetime risk of cirrhosis, increased risk of primary liver cancer and up to 1,000,000 deaths annually. Our long-term objective is to apply our understanding of the resolution of acute HBV infection to the development of effective new immunotherapies for chronic HBV infections. [unreadable] [unreadable] [unreadable]